Elevator Systems
A typical elevator system comprises a rotatably mounted drive sheave supporting a hoist rope, where one end of the hoist rope suspends an elevator cab, and the other end of the hoist rope suspends a counterweight. Upon rotation of the drive sheave, the elevator cab and counterweight translate vertically in opposite directions. The counterweight typically has a weight equal to the weight of the elevator cab plus 42.5 to 50 percent of the rated load capacity (i.e. passengers and cargo) of the elevator system.
Passenger safety plays an important role in the design of elevator systems. Many safety systems have been designed to prevent unintended descent of an elevator cab within an elevator hoistway. This unintended descent may be due to power or mechanical failure within the elevator system, and in some cases, may be due to the severing of ropes that hoist the elevator cab. It is known that without an elevator safety system, unintended descent of an elevator cab may lead to passenger injuries and damage to the elevator cab and hoistway.